diff --git a/packages/core/src/browser/icon-theme-service.ts b/packages/core/src/browser/icon-theme-service.ts
index 7808401e209d5..862890df9718e 100644
--- a/packages/core/src/browser/icon-theme-service.ts
+++ b/packages/core/src/browser/icon-theme-service.ts
@@ -198,9 +198,11 @@ export class IconThemeService {
         const preference = this.schemaProvider.getSchemaProperty(ICON_THEME_PREFERENCE_KEY);
         if (preference) {
             const sortedThemes = Array.from(this.definitions).sort((a, b) => a.label.localeCompare(b.label));
-            preference.enum = sortedThemes.map(e => e.id);
-            preference.enumItemLabels = sortedThemes.map(e => e.label);
-            this.schemaProvider.updateSchemaProperty(ICON_THEME_PREFERENCE_KEY, preference);
+            this.schemaProvider.updateSchemaProperty(ICON_THEME_PREFERENCE_KEY, {
+                ...preference,
+                enum: sortedThemes.map(e => e.id),
+                enumItemLabels: sortedThemes.map(e => e.label)
+            });
         }
     }
 
diff --git a/packages/core/src/browser/preferences/preference-contribution.ts b/packages/core/src/browser/preferences/preference-contribution.ts
index 6c58ef88ffb06..b91b71aff265f 100644
--- a/packages/core/src/browser/preferences/preference-contribution.ts
+++ b/packages/core/src/browser/preferences/preference-contribution.ts
@@ -360,6 +360,10 @@ export class PreferenceSchemaProvider extends PreferenceProvider {
         return this.combinedSchema.properties[key];
     }
 
+    /**
+     * {@link property} will be assigned to field {@link key} in the schema.
+     * Pass a new object to invalidate old schema.
+     */
     updateSchemaProperty(key: string, property: PreferenceDataProperty): void {
         this.updateSchemaProps(key, property);
         this.fireDidPreferenceSchemaChanged();
diff --git a/packages/core/src/browser/theming.ts b/packages/core/src/browser/theming.ts
index 2a8e90b0d68db..ddcc47991ee28 100644
--- a/packages/core/src/browser/theming.ts
+++ b/packages/core/src/browser/theming.ts
@@ -91,9 +91,11 @@ export class ThemeService {
         const preference = this.schemaProvider.getSchemaProperty(COLOR_THEME_PREFERENCE_KEY);
         if (preference) {
             const sortedThemes = this.getThemes().sort((a, b) => a.label.localeCompare(b.label));
-            preference.enum = sortedThemes.map(e => e.id);
-            preference.enumItemLabels = sortedThemes.map(e => e.label);
-            this.schemaProvider.updateSchemaProperty(COLOR_THEME_PREFERENCE_KEY, preference);
+            this.schemaProvider.updateSchemaProperty(COLOR_THEME_PREFERENCE_KEY, {
+                ...preference,
+                enum: sortedThemes.map(e => e.id),
+                enumItemLabels: sortedThemes.map(e => e.label)
+            });
         }
     }